1. Field of the Invention
The present invention relates to a medical system (referred to as a “particle beam therapy system”, hereinafter) that performs therapy by irradiating a charged particle beam (referred to as a “particle beam”, hereinafter), exemplified by a heavy particle beam such as a carbon beam or a proton beam, onto the diseased site of a cancer or the like.
2. Description of the Related Art
Among medical systems that have been developed earlier than particle beam therapy systems and perform therapy by utilizing a radiation such as an X-ray, there has been proposed a medical system that performs therapy of a diseased site evenly with a high dose by irradiating radiations, whose intensity are adjusted, from many directions so that exposure of peripheral tissues is reduced. Here, irradiation onto a diseased site from many directions is referred to as multi-port irradiation.
A number of methods have been proposed for multi-port irradiation; they are exemplified, for example, by IMRT (Intensity-Modulated Radiotherapy: referred Documents 1 and 2 in non-patent document 1), which is proposed mainly by Siemens and in which “step and shoot” is performed, and IMAT (Intensity-Modulated Ark Therapy: referred Document 3 in non-patent document 1), which is proposed mainly by ELEKTA.
In Patent Document 1, there is proposed a radiation irradiation apparatus that is provided with a plurality of compensators for changing the spatial pattern of the X-ray intensity distribution for each irradiation direction so as to apply a high absorption dose only to a diseased site and that performs multi-port irradiation while automatically changing compensators in accordance with irradiation directions.